Just west of Naples, Italy, lies one of the most fascinating and potentially dangerous volcanic regions in Europe.
Unlike Mount Vesuvius, which rises as a recognizable volcanic mountain, Campi Flegrei hides beneath towns, roads, residential neighborhoods, and parts of the Bay of Pozzuoli.
Its name means “Burning Fields,” reflecting the volcanic activity that has shaped the region for thousands of years.
Beneath the surface, powerful geological processes continue to generate earthquakes, ground deformation, and volcanic gases.
Campi Flegrei has experienced enormous prehistoric eruptions, smaller explosive events, and centuries of restless activity.
Its history reveals how a volcanic system can remain active for tens of thousands of years without producing frequent eruptions.
What Is Campi Flegrei?
Campi Flegrei is an extensive volcanic area located in southern Italy, immediately west of Naples.
The region contains numerous volcanic craters, thermal features, and areas of active gas emissions.
Its most important geological structure is a caldera, a large volcanic depression formed when the ground collapses following the withdrawal of substantial quantities of magma during major eruptions.
Unlike a typical cone-shaped volcano, Campi Flegrei consists of a complex network of volcanic structures.
Its caldera extends approximately 12–15 kilometers across, with portions lying beneath the sea.
The volcanic system is closely monitored because densely populated communities occupy parts of its surface.
Campi Flegrei is not one volcanic mountain but an interconnected volcanic landscape with a long history of explosive activity.
The Campanian Ignimbrite Eruption: A Prehistoric Catastrophe
Approximately 39,000 years ago, Campi Flegrei produced one of the largest known volcanic eruptions in European prehistory.
This event is known as the Campanian Ignimbrite eruption.
It released enormous quantities of volcanic ash, gas, and fragmented rock.
Fast-moving currents of hot gas and volcanic debris, known as pyroclastic flows, swept across large areas surrounding the volcano.
Ash from the eruption spread across substantial parts of Europe and the Mediterranean region.
Researchers have identified deposits associated with this event at considerable distances from southern Italy.
The eruption reached approximately magnitude 7 on the Volcanic Explosivity Index.
Its environmental consequences included widespread ash deposition and significant disruption of regional landscapes.
The event occurred during a period of climatic instability, and scientists continue investigating its possible environmental effects.
The Campanian Ignimbrite eruption demonstrates that Campi Flegrei has the geological capacity to produce extraordinarily powerful explosive events.
The Neapolitan Yellow Tuff Eruption
Around 15,000 years ago, Campi Flegrei experienced another major explosive eruption.
Known as the Neapolitan Yellow Tuff eruption, this event significantly reshaped the volcanic landscape.
Large quantities of ash and volcanic material accumulated across the surrounding region.
Over time, some deposits hardened into yellowish volcanic rock.
This material later became an important construction resource in Naples and nearby settlements.
The eruption also contributed to the development of the present caldera structure.
Although smaller than the Campanian Ignimbrite event, it was still an exceptionally powerful volcanic explosion.
Its deposits provide valuable information about the evolution of the volcanic system.
Thousands of Years of Smaller Eruptions
After the Neapolitan Yellow Tuff eruption, Campi Flegrei did not become permanently inactive.
Instead, numerous smaller volcanic eruptions occurred across different parts of the caldera.
These events created cones, craters, and layers of volcanic deposits.
One notable eruption occurred at Agnano-Monte Spina approximately 4,100 years ago.
Other eruptions formed features such as the Astroni volcanic complex.
Many of these events involved interactions between rising magma and underground or surface water.
Such interactions can generate phreatomagmatic eruptions, in which rapidly expanding steam contributes to explosive fragmentation of volcanic material.
This history reveals an important characteristic of Campi Flegrei.
Volcanic activity can migrate between different locations within the same caldera rather than repeatedly emerging from a single central crater.
The 1538 Eruption: Birth of Monte Nuovo
The most recent known eruption of Campi Flegrei occurred in 1538.
It began on September 29 near the town of Pozzuoli.
Residents experienced earthquakes and significant ground deformation before the eruption.
Explosions then released ash and volcanic fragments, rapidly building a new volcanic cone.
The formation became known as Monte Nuovo, meaning “New Mountain.”
The eruption continued for approximately one week.
Within days, a new volcanic hill had appeared in an area previously occupied by relatively low terrain.
This event is especially important because written historical accounts describe the eruption and the changes that preceded it.
Monte Nuovo provides direct historical evidence that Campi Flegrei can return to eruptive activity after centuries of relative quiet.
Why the Ground Rises and Falls
One of the most unusual features of Campi Flegrei is the gradual movement of the ground.
This phenomenon is called bradyseism.
It involves periods of uplift and subsidence caused by changing pressures and processes beneath the surface.
The ancient Roman structures at Pozzuoli provide remarkable evidence of these movements.
Marine organisms left traces on columns that were once submerged beneath seawater.
Later, the land rose again.
Modern instruments have recorded repeated uplift episodes, including major unrest during 1969–1972 and 1982–1984.
Since 2005, the region has experienced another prolonged phase of uplift.
These movements can damage buildings, roads, and underground infrastructure.
Earthquakes and Volcanic Unrest
Campi Flegrei regularly experiences small earthquakes.
Sometimes these occur in concentrated sequences known as a seismic swarm.
Such activity can result from stress changes, rock fracturing, and pressure variations within the volcanic system.
Earthquakes have become an important concern for communities around Pozzuoli and western Naples.
However, an increase in seismic activity does not automatically mean that an eruption is imminent.
Scientists must interpret earthquakes together with ground movement, gas emissions, and other measurements.
The challenge is distinguishing normal variations in volcanic unrest from changes that might indicate a greater possibility of eruptive activity.
Solfatara and the Signs of Underground Heat
One of Campi Flegrei’s best-known volcanic features is Solfatara.
This crater contains areas where hot gases escape through openings called fumaroles.
These emissions include water vapor, carbon dioxide, and sulfur-containing gases.
The nearby Pisciarelli area also exhibits intense hydrothermal activity.
Scientists investigate these gases because changes in temperature, composition, and emission rates may provide information about underground processes.
However, volcanic gases also create safety hazards.
High concentrations of carbon dioxide can accumulate in poorly ventilated low-lying locations.
Expert Perspective: Understanding Volcanic Risk
Italian volcanologist Giuseppe De Natale has extensively researched Campi Flegrei, including its volcanic history, ground deformation, and seismic activity.
His scientific work contributes to understanding how pressure changes and geological structures influence volcanic unrest.
A central principle of modern volcanology is that volcanic monitoring requires multiple independent observations.
Earthquakes, surface deformation, and changes in gas emissions must be evaluated together.
No single measurement can reliably predict the exact time, location, or magnitude of a future volcanic eruption.
How Scientists Monitor Campi Flegrei
Italy’s National Institute of Geophysics and Volcanology operates extensive monitoring networks in the region.
Researchers use several techniques:
- Seismometers to record earthquakes
- Satellite measurements to detect ground deformation
- GPS stations to track surface movement
- Instruments that measure volcanic gases
- Temperature and geochemical monitoring of hydrothermal areas
These observations support scientific assessments and emergency planning.
Authorities use a volcanic alert level system to communicate different stages of volcanic unrest.
Monitoring information helps guide preparedness, although it cannot eliminate uncertainty.
Could Campi Flegrei Erupt Again?
Campi Flegrei remains an active volcanic system, and future eruptions are possible.
Its geological history includes volcanic activity of very different magnitudes.
Potential hazards include ashfall, explosive activity, hot pyroclastic currents, gas emissions, and earthquake-related damage.
The risks depend on the eruption’s location, intensity, and development.
Because large populations live near the volcanic system, emergency planning is especially important.
P.S. Given the significant increase in volcanic activity over the past century, I strongly urge you to get as far away from the caldera area as possible before the situation worsens. We do not know how a potential future eruption might unfold, and if—God forbid—a major earthquake were to strike the region, there might be no time left to evacuate…
Interesting Facts
- Campi Flegrei means “Burning Fields.”
- The volcanic system is located immediately west of Naples, with part of its caldera extending beneath the sea.
- Its Campanian Ignimbrite eruption occurred approximately 39,000 years ago.
- The Neapolitan Yellow Tuff eruption occurred around 15,000 years ago.
- Monte Nuovo formed during the eruption of 1538, the most recent known eruption of Campi Flegrei.
- Ancient Roman columns at Pozzuoli preserve evidence of historical changes in sea level relative to the land.
- Ground uplift has occurred repeatedly without producing a volcanic eruption.
- Scientists continuously monitor earthquakes, ground deformation, and gas emissions to evaluate volcanic unrest.
- The term supervolcano is informal and does not mean that every future eruption must be exceptionally large.
Glossary
- Caldera — A large volcanic depression formed when the ground collapses following the withdrawal of substantial quantities of magma.
- Campanian Ignimbrite — The deposits and associated major explosive eruption of Campi Flegrei approximately 39,000 years ago.
- Pyroclastic Flows — Rapidly moving currents of hot volcanic gas, ash, and rock fragments.
- Neapolitan Yellow Tuff — A widespread volcanic rock deposit formed during a major Campi Flegrei eruption approximately 15,000 years ago.
- Magma — Molten or partially molten rock beneath Earth’s surface.
- Phreatomagmatic Eruptions — Explosive volcanic events involving interactions between magma and water.
- Bradyseism — Gradual ground uplift or subsidence associated with changes in pressure and processes beneath a volcanic region.
- Seismic Swarm — A sequence of earthquakes occurring close together in space and time without a clearly dominant mainshock.
- Fumaroles — Openings in Earth’s surface through which volcanic gases and steam escape.
- Volcanic Alert Level — An official classification used to communicate the assessed state of volcanic activity or unrest.
